The overall objective of this research program is to use the targeted expression of heterologous genes to manipulate brain dopaminergic systems. This proposal takes advantage of the recent cloning of the cDNA for several neurotransmitter transporters. Two considerations comprise the rationale for this work. First, the available data indicate that the dopamine transporter (DAT) is expressed only in dopaminergic neurons. Indeed, the dopamine transporter may be the only protein whose expression is limited to dopaminergic neurons. Thus, the promoter region of the dopamine transporter will be a unique tool for the analysis of the function of the dopamine system, and a potential tool for gene therapy, because it will be possible to target expression of a heterologous protein selectively to dopaminergic neurons. The second consideration is the importance of the dopamine system in a variety of disorders including schizophrenia, parkinsonism and drug abuse. The specific aims of this proposal are based on two guiding hypotheses: 1) Cell specific expression of the dopamine transporter is determined by cis-acting elements in the 5' flanking region of the gene. The experiments proposed will also determine if critical regulatory elements are present that are not in the 5' flanking region. 2) It will be possible to define a transcriptional regulatory domain of the dopamine transporter gene that will target strong expression of a heterologous protein selectively to dopaminergic neurons. The specific aim of the application is to identify genomic elements that determine dopaminergic cell-specific expression in transgenic mice.